Equalizers are commonly used in wireless communications systems. In order to perform equalization in environments with a large delay spread, the equalizer span must grow quite large, which results in a significant increase in complexity. Additionally, a problem of performing macro diversity combining with an equalizer-based architecture exists in conventional wireless communication systems.
One solution for equalizing signals that have passed through large delay spread channels or those received from multiple Node-Bs, (e.g., for macro diversity), is a Rake-based solution. However, Rake-based solutions do not, in general, provide sufficient cross path interference cancellation for low spreading factor data channels, such as those used in a high speed downlink packet access (HSDPA) service. Without sufficient cross path interference cancellation, the performance of a receiver may not be acceptable for HSDPA.
Conventional wireless communication systems require a hybrid Rake/equalizer solution which cannot share hardware and/or software resources. This is due to the fact that, as completely different algorithms, they have few data processing operations in common. In accordance with the release 4 (R4) universal mobile telecommunication services (UMTS) frequency division duplex (FDD) standards, any receiver must be tolerant of large delay spread channels, (e.g., >20 μs), and be capable of performing combining of signals from multiple Node-Bs.